\documentclass{standalone}
\usepackage{tikz,ctex,siunitx,mhchem}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{pgfplots}
\pgfplotsset{
	width=9cm, 
  height=6cm,
  compat=1.17,
  every tick label/.append style={font=\scriptsize},
  every axis label/.append style={font=\footnotesize},
  legend style={font=\footnotesize},  
}
\pgfkeys{/pgf/number format/.cd,fixed,min exponent for 1000 sep=4}
\tikzstyle{every pin}=[font=\tiny,inner sep=0pt]
\begin{document}
  \begin{tikzpicture}
    \begin{axis}[
      % axis lines=left,
      xtick={0,50,...,250},
      % xtick style={at={(yticklabel cs:0,5pt)}},
      ytick={0,2,...,10},
      ylabel=平均结合能/\unit{MeV},
      y label style={at={(0,1)},rotate=-90,anchor=south west},
      xlabel=质量数/$A$,
      x label style={at={(1,0)},anchor=south west},
      xmajorgrids,
      ymajorgrids,
      xminorgrids,
      yminorgrids,
      minor y tick num=1,
      minor x tick num=4,
      ymin=0,ymax=10,
      xmin=0,xmax=250,
      major grid style={brown!70!white,very thin},
      minor grid style={brown!50!white,ultra thin,densely dashed},
      % bar width=7pt,
      % x tick label style={rotate=90,anchor=east},
      % nodes near coords,
      nodes near coords style={font=\scriptsize},
      % nodes near coords align={vertical},
      % legend style={at={(0,1)},anchor=north west},
	  	]
      \addplot [blue,text=black,
        only marks,mark size=0.7pt,
      ] 
      coordinates 
      {
        (3.050,1.125)(4.400,7.125)(7.250,5.673)(8.500,6.553)
        (11.550,7.703)(13.100,7.043)(14.650,7.505)(14.650,7.673)
        (16.250,7.873)(17.000,8.025)(18.500,7.785)(20.200,8.105)
        (22.250,8.205)(26.500,8.458)(27.800,8.625)(31.250,8.535)
        (34.600,8.633)(37.550,8.735)(40.100,8.638)(55.800,8.860)
        (62.250,8.895)(75.400,8.870)(83.800,8.905)(85.750,8.853)
        (96.050,8.830)(115.850,8.698)(117.050,8.588)(121.000,8.715)
        (122.550,8.598)(129.800,8.510)(135.850,8.603)(143.100,8.428)
        (149.250,8.328)(174.350,8.155)(181.200,8.065)(182.600,8.135)
        (184.200,8.053)(192.600,8.053)(194.100,8.128)(206.100,7.950)
        (232.000,7.778)(238.000,7.690)
      }
      node [inner sep=0pt,pos=0, pin=0:\ce{^2H}] {}
      node [inner sep=0pt,pos=0.03, pin=87:\ce{^4He}] {}
      node [inner sep=0pt,pos=0.05, pin=280:\ce{^6Li}] {}
      node [inner sep=0pt,pos=0.07, pin=280:\ce{^9Be}] {}
      node [inner sep=0pt,pos=0.09, pin=60:\ce{^12C}] {}
      node [inner sep=0pt,pos=0.17, pin=-45:\ce{^14C}] {}
      node [inner sep=0pt,pos=0.22, pin=-30:\ce{^16O}] {}
      node [inner sep=0pt,pos=0.98, pin=120:\ce{^235U}] {}
      ;
      \draw[semithick,red,line join=round](3.050,1.125)--(4.400,7.125)--(7.250,5.673)--(8.500,6.553)--(11.550,7.703)--(13.100,7.043)..controls( 13.650,7.558)and( 20.300,8.858)..( 61.200,8.905)..controls( 84.450,8.983)and(135.700,8.555)..      (136.850,8.525)..controls(142.800,8.448)and(254.850,7.620)..(254.850,7.620);
      % \draw[<-](232.000,7.778)--++(45:0.5);
		\end{axis}
  \end{tikzpicture}
\end{document}